The present disclosure relates to an image pickup element having a photoelectric conversion section including a chalcopyrite-based compound. The present disclosure also relates to an image pickup device including the image pickup element.
In a solid-state image pickup device such as a charge coupled device (CCD) image sensor and a complementary metal oxide semiconductor (CMOS) image sensor, a solid-state image pickup element (an image pickup element) including a photoelectric conversion section is disposed for each pixel. The photoelectric conversion section of the image pickup element may be configured of, for example, a semiconductor material such as silicon (Si). On a surface of the photoelectric conversion section, crystal defects and dangling bonds are present due to breaking of a crystal structure. The crystal defects and the dangling bonds lead to extinction, due to recombination, of an electron-hole pair generated in the photoelectric conversion section, or lead to generation of a dark current. In particular, short-wavelength light is absorbed in proximity to the surface of the photoelectric conversion section to cause generation of an electron-hole pair, and therefore is greatly affected, which leads to a decrease in sensitivity for the short-wavelength light.
On the other hand, the generation of the dark current occurs due to spreading of a depletion layer to a surface interface of the photoelectric conversion section, in addition to the presence of the crystal defects and the dangling bonds on the surface of the photoelectric conversion section. The depletion layer may be controlled by, for example, performing ion implantation in a case of Si. Therefore, for example, in a solid-state image pickup element using Si, an embedded-type photodiode, in which p-type and n-type impurity densities are controlled by ion implantation, may be used for the photoelectric conversion section. In addition, for example, in a photoelectric conversion element of Japanese Unexamined Patent Application Publication No. 2012-129250, a layer made of a material with a band gap wider than that of Si is formed on a surface of a Si layer included in a photoelectric conversion section. As a result, occurrence of an electron-hole pair at a surface of the photoelectric conversion section is suppressed.
Further, in addition to downsizing and higher sensitivity, higher image quality is demanded of the image pickup devices. To achieve the higher image quality, a decrease in generation of a dark current is necessary. For example, in a solid-state image pickup device of Japanese Unexamined Patent Application Publication No. 2012-4443, sensitivity is increased by reducing a dark current through use of a chalcopyrite-based compound semiconductor as a photoelectric conversion film on a silicon substrate.